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BoatWorks: A Sticky Through-hull

It’s hard to make a hole smaller, but sometimes it’s just as hard to make it bigger, I thought as I stared at the through-hull fittings for my galley sink drain. I had just installed a new Isotherm fridge, and now I needed to install its SP water-cooling system. This required removing the existing galley drain through-hull and seacock and replacing it with the SP through-hull, which was almost an inch wider.

Having been embedded in the hull for 30-plus years, the existing through-hull was hard to access from the inside and definitely wanted to stay put. I could have removed it easily enough by making a series of careful cuts through the bronze walls of the through-hull from the outside with a Sawzall, then knocking the pieces out from the inside. But then I’d be left with a hole that was still too small for the SP system. Since the solid fiberglass hull was almost an inch thick at the point in question, it would have taken ages to ream out the hole to the correct size.

Then inspiration struck. I measured the through-hull’s flush-fitting flange and found it was almost exactly the same size as the body of the new through-hull fitting. With the right-sized hole saw, I could drill out the entire fitting and the new one would slot right in. On the down side, with nothing for the hole saw’s pilot drill bit to bite into, it would be nearly impossible to make a neat job of it. But then I remembered the wooden bungs I keep on board to hammer into leaky seacocks. A couple of hearty blows from my ball-peen hammer drove one home, and I sawed off the protruding end flush with the through-hull.

Finding the center of the wooden plug was but a moment’s work and soon the air was filled with fiberglass dust as a hole saw chucked on to my 120V drill ate through the hull. Within a minute the through-hull (along with its seacock) was out.